1. Keyboard
The keyboard is the most widely used input device and is used to enter data or commands to the computer. It has a set of alphabet keys, a set of digit keys, and various function keys and is divided into four main areas:
- Function keys across the top
- Letter keys in the main section
- A numeric keypad on the right
- Cursor movement and editing keys between the main section and the numeric keypad.
Some keyboards come with added keys for using the Internet and others have an integrated wrist support. Ergonomic keyboards have been developed to reduce the risk of repetitive strain injury to workers who use keyboards for long periods of time.
The computer's processor scans the keyboard hundreds of times per second to see if a key has been pressed. When a key is pressed, a digital code is sent to the Central Processing Unit (CPU). This digital code is translated into ASCII code (American Standard Code of Information Interchange).
For example, pressing the 'A' key produces the binary code 01100001 representing the lower case letter 'a'. Holding down the shift key at the same time produces the binary code 01000001 representing the upper case letter 'A'.
Advantages:
- Most computers have this device attached to it
- It is a reliable method for data input of text and numbers
- A skilled typist can enter data very quickly.
- Specialist keyboards are available
- It is very easy to make mistakes when typing data in
- It can be very time consuming to enter data using a keyboard, especially if you are not a skilled typist.
- It is very difficult to enter some data, for example, details of diagrams and pictures.
- It is very slow to access menus and not flexible when you want to move objects around the screen
- Difficult for people unable to use keyboards through paralysis or muscular disorder.
2. Mouse
A mouse is the most common pointing device that you will come across. It enables you to control the movement and position of the on-screen cursor by moving it around on the desk.
Buttons on the mouse let you select options from menus and drag objects around the screen. Pressing a mouse button produces a 'mouse click'. You might have heard the expressions 'double click', 'click and drag' and 'drag and drop'.
Most mice use a small ball located underneath them to calculate the direction that you are moving the mouse in. The movement of the ball causes two rollers to rotate inside the mouse; one records the movement in a north-south direction and the other records the east-west movement. The mouse monitors how far the ball turns and in what direction and sends this information to the computer to move the pointer.
Advantages:
- Ideal for use with desktop computers.
- Usually supplied with a computer so no additional cost.
- All computer users tend to be familiar with using them.
Disadvantages:
- They need a flat space close to the computer.
- The mouse cannot easily be used with laptop, notebook or palmtop
- computers. (These need a tracker ball or a touch sensitive pad called a touch pad).
3. Trackball
A tracker ball is like an upside down mouse with the ball on top. Turning the ball with your hand moves the pointer on the screen. It has buttons like a standard mouse, but requires very little space to operate and is often used in conjunction with computer aided design. You will often find a small tracker ball built into laptop computers in place of the conventional mouse.
Advantages:
- Ideal for use where flat space close to the computer is limited.
- Can be useful with laptops as they can be built into the computer keyboard or clipped on.
Disadvantages:
- Not supplied as standard so an additional cost and users have to learn how to use them
4. Joystick
A Joystick is similar to a tracker ball in operation except you have a stick which is moved rather than a rolling ball.Joysticks are used to play computer games. You can move a standard joystick in any one of eight directions. The joystick tells the computer in which direction it is being pulled and the computer uses this information to (for example) move a racing car on screen. A joystick may also have several buttons which can be pressed to trigger actions such as firing a missile.
Advantages:
- There is an immediate feel of direction due to the movement of the stick
Disadvantages:
- Some people find the joystick difficult to control rather than other point and click devices. This is probably because more arm and wrist movement is required to control the pointer than with a mouse or tracker ball.
- Joysticks are not particularly strong and can break easily when used with games software.
5. Touch Screen
These screens do a similar job to concept keyboards. A grid of light beams or fine wires criss-cross the computer screen. When you touch the screen with your finger, the rays are blocked and the computer 'senses' where you have pressed. Touch screens can be used to choose options which are displayed on the screen.
Touch screens are easy to use and are often found as input devices in public places such as museums, building societies (ATMs), airports or travel agents. However, they are not commonly used elsewhere since they are not very accurate, tiring to use for a long period and are more expensive than alternatives such as a mouse.
Advantages:
- Easy to use
- Software can alter the screen while it is running, making it more flexible that a concept keyboard with a permanent overlay
- No extra peripherals are needed apart from the touch screen monitor itself.
- No experience or competence with computer systems are needed to be able to use it.
Disadvantages:
- Not suitable for inputting large amounts of data
- Not very accurate, selecting detailed objects can be difficult with fingers
- Tiring to use for a long period of time
- More expensive than alternatives such as a mouse.
- Touch screens are not robust and can soon become faulty.
6. Digital Camera
A digital camera looks very similar to a traditional camera. However, unlike photographic cameras, digital cameras do not use film. Inside a digital camera is an array of light sensors. When a picture is taken, the different colors that make up the picture are converted into digital signals (binary) by sensors placed behind the lens.
Most digital cameras let you view the image as soon as you have taken the picture and, if you don't like what you see, it can be deleted. The image can then be stored in the camera's RAM or on a floppy disk. Later, the pictures can be transferred onto a computer for editing using photo imaging software.
The amount of memory taken up by each picture depends on its resolution. The resolution is determined by the number of dots which make up the picture: the greater the number of dots which make up the picture, the clearer the image. However, higher resolution pictures take up more memory (and are more expensive!).
Resolution range from about 3 million (or Mega) pixels up to 12 Mega pixels Digital cameras are extremely useful for tasks such as producing newsletters. There is often a digital camera built into mobile phones that operates in exactly the same way as a standard one.
Advantages:
- No film is needed and there are no film developing costs
- Unwanted images can be deleted straight away
- You can edit, enlarge or enhance the images
- Images can be incorporated easily into documents, sent by e-mail or added to a website.
Disadvantages:
- Digital cameras are generally more expensive than ordinary cameras.
- Images often have to be compressed to avoid using up too much expensive memory
- When they are full, the images must be downloaded to a computer or deleted before any more can be taken.
7. Scanner
A scanner is another way in which we can capture still images or text to be stored and used on a computer. Images are stored as 'pixels'. A scanner works by shining a beam of light on to the surface of the object you are scanning. This light is reflected back on to a sensor that detects the color of the light.
The reflected light is then digitized to build up a digital image. Scanner software usually allows you to choose between a high resolution (very high quality images taking up a lot of memory) and lower resolutions. Special software can also be used to convert images of text into actual text data which can be edited by a word processor. This software is called an "Optical Character Reader" or OCR.
There are two types of scanner:
- Flatbed Scanner
- Handheld Scanner
The most popular type of scanner is the flatbed. It works in a similar way to a photocopier. Flatbed scanners can scan larger images and are more accurate than handheld scanners.
Handheld scanners are usually only a few inches wide and are rolled across the document to be scanned. They perform the same job but the amount of information that can be scanned is limited by the width of the scanner and the images produced are not of the same quality as those produced by flatbed scanners.
Advantages:
- Flat-bed scanners are very accurate and can produce images with a far higher resolution than a digital camera
- Any image can be converted from paper into digital format and later enhanced and used in other computer documents.
Disadvantages:
- Images can take up a lot of memory space.
- The quality of the final image depends greatly upon the quality of the original document.
8. Graphics tablets
Graphics tablets are often used by graphics designers and illustrators. Using a graphics tablet a designer can produce much more accurate drawings on the screen than they could with a mouse or other pointing device. A graphics tablet consists of a flat pad (the tablet) on which you draw with a special pen. As you draw on the pad the image is created on the screen. By using a graphics tablet a designer can produce very accurate on-screen drawings.
Drawings created using a graphics tablet can be accurate to within hundredths of an inch. The 'stylus' or pen that you use may have buttons on it that act like a set of mouse buttons. Sometimes, instead of a stylus a highly accurate mouse-like device called a puck is used to draw on the tablet.
Advantages:
- In a design environment where it is more natural to draw diagrams with pencil and paper, it is an effective method of inputting the data
- into the computer.
Disadvantages:
- Not as good as a mouse for clicking on menu items.
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